Over the recent years, high-efficiency transmission based on digitalization has been adopted frequently in wireless communications. What is important in the case of applying a multi-valued phase modulation method to the wireless communications is a technology of restraining a nonlinear distortion by linearizing especially an amplifying characteristic of a power amplifier for transmission on a transmission side and reducing adjacent-channel leakage power. Further, a case of contriving to improve power efficiency by use of an amplifier exhibiting inferior linearity involves employing a technology for compensating the nonlinear distortion.
A digital nonlinear distortion compensation method is known as the distortion compensation technology. The digital nonlinear distortion compensation method is a method of feedback-detecting carrier waves obtained by orthogonal modulation using modulation signals, converting the modulation signal (transmission baseband signal) and a feedback signal (feedback baseband signal) into digital signals, then comparing these digital signals, and updating a distortion compensation coefficient on the basis of a result of this comparison.